The present invention relates generally to filtering devices and systems which can be used when an interventional procedure is being performed in a stenosed or occluded region of a blood vessel to capture embolic material that may be created and released into the bloodstream during the procedure. The system of the present invention is particularly useful when performing balloon angioplasty, stenting procedures, laser angioplasty, atherectomy, or other interventional procedures in critical vessels, particularly in vessels such as the carotid arteries, where the release of embolic debris into the bloodstream can occlude the flow of oxygenated blood to the brain or other vital organs, which can cause devastating consequences to the patient. While the embolic protection system of the present invention is particularly useful in carotid procedures, the invention can be used in conjunction with any vascular interventional procedure in which there is an embolic risk.
A variety of non-surgical interventional procedures have been developed over the years for opening stenosed or occluded blood vessels in a patient caused by the build up of plaque or other substances on the wall of the blood vessel. Such procedures usually involve the percutaneous introduction of the interventional device into the lumen of the artery, usually through a catheter. In typical carotid PTA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral artery and advanced through the vasculature until the distal end of the guiding catheter is in the common carotid artery. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s carotid vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
Another procedure is laser angioplasty which utilizes a laser to ablate the stenosis by super heating and vaporizing the deposited plaque. Atherectomy is yet another method of treating a stenosed blood vessel in which cutting blades are rotated to shave the deposited plaque from the arterial wall. A vacuum catheter is usually used to capture the shaved plaque or thrombus from the blood stream during this procedure.
In the procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. The stent is crimped tightly onto the balloon portion of the catheter and transported in its delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter.
Prior art stents typically fall into two general categories of construction. The first type of stent is expandable upon application of a controlled force, as described above, through the inflation of the balloon portion of a dilatation catheter which, upon inflation of the balloon or other expansion means, expands the compressed stent to a larger diameter to be left in place within the artery at the target site. The second type of stent is a self-expanding stent formed from, for example, shape memory metals or super-elastic nickel-titanum (NiTi) alloys, which will automatically expand from a collapsed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen. Such stents manufactured from expandable heat sensitive materials allow for phase transformations of the material to occur, resulting in the expansion and contraction of the stent.
The above non-surgical interventional procedures, when successful, avoid the necessity of major surgical operations. However, there is one common problem which can become associated with all of these non-surgical procedures, namely, the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible that the metal struts of the stent can cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient""s vascular system. Pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream. Additionally, while complete vaporization of plaque is the intended goal during a laser angioplasty procedure, quite often particles are not fully vaporized and thus enter the bloodstream. Likewise, not all of the emboli created during an atherectomy procedure may be drawn into the vacuum catheter and, as a result, enter the bloodstream as well.
When any of the above-described procedures are performed in the carotid or arteries, the release of emboli into the circulatory system can be extremely dangerous and sometimes fatal to the patient. Debris that is carried by the bloodstream to distal vessels of the brain can cause these cerebral vessels to occlude, resulting in a stroke, and in some cases, death. Therefore, although cerebral percutaneous transluminal angioplasty has been performed in the past, the number of procedures performed has been limited due to the justifiable fear of causing an embolic stroke should embolic debris enter the bloodstream and block vital downstream blood passages.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system following vessel treatment utilizing any one of the above-identified procedures. One approach which has been attempted is the cutting of any debris into minute sizes which pose little chance of becoming occluded in major vessels within the patient""s vasculature. However, it is often difficult to control the size of the fragments which are formed, and the potential risk of vessel occlusion still exists, making such a procedure in the carotid arteries a high-risk proposition.
Other techniques which have been developed to address the problem of removing embolic debris include the use of catheters with a vacuum source which provides temporary suction to remove embolic debris from the bloodstream. However, as mentioned above, there have been complications with such systems since the vacuum catheter may not always remove all of the embolic material from the bloodstream, and a powerful suction could cause problems to the patient""s vasculature. Other techniques which have had some limited success include the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. However, there have been problems associated with filtering systems, particularly during the expansion and collapsing of the filter within the body vessel. If the filtering device does not have a suitable mechanism for closing the filter, there is a possibility that trapped embolic debris can backflow through the inlet opening of the filter and enter the blood-stream as the filtering system is being collapsed and removed from the patient. In such a case, the act of collapsing the filter device may actually squeeze trapped embolic material through the opening of the filter and into the bloodstream.
Some of the prior art filters which can be expanded within a blood vessel are attached to the distal end of a guide wire or guide wire-like tubing which allows the filtering device to be placed in the patient""s vasculature when the guide wire is manipulated in place. Once the guide wire is in proper position in the vasculature, the embolic filter can be deployed within the vessel to capture embolic debris. The guide wire can then be used by the physician to deliver interventional devices, such as a balloon angioplasty dilatation catheter or a stent, into the area of treatment.
While expandable filters placed on the distal end of a guide wire or guide wire like catheter are generally capable of reaching many stenosis in a patient""s vasculature, there still can be some instances encountered by a physician in which the guide wire cannot reach or cross a particularly tight distal lesion. This can sometimes occur when the expandable filter device is to be placed across a tight lesion in the distal carotid arteries when a femoral approach is taken by the physician. In those cases, the physician often can steer the filter device to a location close to the area of treatment, but cannot cross the lesion for one reason or another. Some physicians deal with this situation by removing the filter device from the patient""s vasculature and attempting to cross the lesion using a separate guide wire which can be used to somewhat straighten the body vessel, making it easier for the physician to re-attempt the placement of the filter device across the lesion. In such cases, the physician is required to maneuver the steerable filter device back to the area of treatment to re-attempt the crossing of the lesion. The filter device may be then able to cross the lesion and be placed downstream of the area of treatment to capture any embolic debris which can may be created during the subsequent interventional procedure. However, this procedure causes the physician to perform additional steps which are time-consuming due to the increased number of times that the physician has to maneuver the filtering device and additional guide wire into the patient""s vasculature.
What has been needed is a reliable system for use with an expandable filter device which allows the physician to steer through tortuous anatomy to distal lumens where the filtering device can be deployed to capture or remove embolic debris from the bloodstream. The system should be relatively easy for a physician to use and should provide a suitable delivery system for placing a filtering device into distal and tight lesions of a patient""s anatomy. Moreover, the system should be relatively easy to deploy and remove from the patient""s vasculature. The invention disclosed herein satisfies these and other needs.
The present invention provides a delivery system which can be utilized to place an expandable filter device past a distal lesion in a patient""s vasculature in order to capture embolic debris which may be created during the performance of a therapeutic intereventional procedure, such as a balloon angioplasty or stenting procedure, in order to prevent embolic debris from entering the bloodstream and blocking vessels downstream from the area of treatment. The present invention can be used in conjunction with either a steerable or non-steerable expandable filtering device. The present invention eliminates the need for a physician to remove and re-insert the expandable filtering device in the patient since a separate guide wire is utilized to reach the desired area of treatment. The system creates an over-the-wire delivery system for placing the expandable filter device in the area of treatment. As a result, the present invention should eliminate additional steps when placing an expandable filtering device into certain distal locations in a patient""s vasculature.
In one aspect of the present invention, a dual lumen delivery sheath is used with an expandable filter device and a separate guide wire as the delivery system. The dual lumen delivery sheath can be made from an elongate tubular member which is adapted to receive both the expandable filter device and the guide wire which can be used as a primary component for placing the filtering device into the area of treatment. In one aspect of the present invention, two separate lumens are formed in the delivery sheath, one for receiving the expandable filtering device and the other for the primary guide wire. In this arrangement, the primary guide wire is extendable within its own separate lumen so that it can be maneuvered by the physician through the tortuous anatomy of the patient into the area of treatment. The delivery sheath can be placed into the area of treatment using over-the-wire techniques which places both the delivery sheath and the expandable filter device past the lesion to be treated. Thereafter, the primary guide wire can be removed from the patient""s vasculature with the delivery sheath and expandable filter device remaining in place downstream from the area of treatment. The delivery sheath can then be retracted to allow the expandable filter device to move into its expanded condition within the body lumen where it will be deployed for capturing any embolic debris which may be collected during the subsequent interventional procedure. If the filter device is mounted on its own guide wire, an interventional device can be delivered into the area of treatment using over-the-wire techniques.
In another aspect of the invention, the guide wire lumen extends along the entire length of the delivery sheath. Alternatively, a rapid exchange type delivery sheath can be created which utilizes only a short segment which receives the primary guide wire. Usually, the guide wire segment is located at the distal end of the delivery sheath to ensure that both the distal ends of the sheath and filter device will properly track along the primary guide wire. In another aspect of the present invention, the distal end of the filter lumen has a smaller diameter than the collapsed filter device to prevent the filter device from entering into the guide wire lumen until the expandable filter device is ready to be deployed within the patient""s vasculature. This narrow lumen helps prevent the primary guide wire and filter device from possibly becoming xe2x80x9ctangledxe2x80x9d during delivery with the patient""s vasculature. The narrow portion of the lumen should not affect the ability of the sheath to be retracted over the collapsed filter device since the narrower lumen should stretch somewhat over the filter device. Alternatively, the narrow portion of the sheath may be scored or provided with one or more lines of perforations which will cause the sheath to split a controlled amount making it easier to retract the sheath over the filter device.
The filter lumen of the present invention also can be made from a short segment to create a rapid exchange type delivery sheath. In one aspect, the filter lumen would be created from a short segment formed adjacent to the guide wire lumen. In an alternative design, both the guide wire lumen and filter lumen could be short segments forming a rapid exchange type sheath. The sheath could be mounted to a mandrel or third wire which would be used to retract the sheath from the expandable filter.
The delivery sheath made in accordance with the present invention also can be provided with a slit extending substantially along the length of the sheath to provide a slotted exchange sleeve which facilitates exchanges of the delivery sheath during use. As a result, the time needed to remove the delivery sheath from the patient""s vasculature can be reduced.
In an alternative delivery design, the primary guide wire can be utilized in accordance with an expandable filter device which utilizes an obturator for delivering the filter device within the patient""s vasculature. An obturator is generally a tapered tip made from a soft pliable material which creates an atraumatic tip which helps prevent trauma from being inflicted on the walls of the patient""s vasculature as the filter device is being steered therethrough. In this aspect of the present invention, the obturator is equipped with a lumen through which the primary guide wire can extend to provide an over-the-wire delivery system that is easy to operate. The guide wire lumen on the obturator could be either set off center from the distal tip of the obturator or could extend substantially through the center portion of the tip of the obturator. In use, the entire filter device, including its own delivery sheath, rides over the primary guide wire (via the guide wire lumen of the obturator) and into the desired area of deployment within the patient""s vasculature.
These and other inventions of the present invention will become more apparent from the following detailed description, when taken in conjunction with the accompanying exemplary drawings.